Respiratory canisters and associated filling methods are known. Such respiratory canisters are often used for providing air purification of contaminated environments to protect workers, first responders, and warfighters. Air purification of vapors and gases is effected by activated materials, typically granular activated carbon, crystalline materials such as zeolites, metal oxides, or metallic organic frameworks, silica gel, and molecular sieves. These activated materials or “sorbents” must be contained in a cavity within the canister through which the contaminated air is passed. Granular sorbent particulate matter is a homogeneous material of defined unit volume within which exist multi-modal distributions of particles with varying physical properties, such as diameter, surface area, hardness, and particle density.
The filling of the canister cavity determines the effective utilization of the sorbent material contained therein. It is desirable to use the least sorbent material possible in order to minimize the size, weight, breathing resistance and commercial cost of the canister.
Traditional two-axis vibrational filling techniques impart fractional gravitational forces to maximize the effective packed bed density of the resultant bed while preventing full vibrofluidization of the sorbent bed during filling. The use of vibration imparts force on the particle through the sorbent bed walls and nearest neighbor sorbent particles. Empirical evidence demonstrates for these techniques that vibrational acceleration in the horizontal direction of about 0.48 g and vibration acceleration in a vertical direction of about 0.45 g achieves a desired packing density.
Techniques such as these are suboptimal in that the target packing density is in reference to that achieved with a snowstorm or raining technique that is less than the theoretical maximum achievable packing density based on the mean diameter, sphericity, and particle diameter of the sorbent. Furthermore the vibrational force impacted onto the particles is dampened in stages, from the controlled force, by the nearest neighbor particles and resultant partial sorbent bed. In the first stage of this filling technique the particles contact directly with the sorbent bed exit screen. As stable packing density is achieved by particles, movement is first constrained then ceases in the vertical direction. Similarly, a localized horizontal effect is achieved. This maximizes the forces impacted onto the particles nearest to the sorbent bed exit screen and sidewalls and minimizes the forces nearest to the sorbent introduction point.
To achieve sufficient force to achieve a minimally acceptable density in these regions higher than desired force is impacted onto the sorbent bed exit screen and side wall regions. This produces a classifying effect whereby particles with higher packed density (smaller diameter) are deposited in the higher force regions, while particles with lower packed density (larger diameter) are deposited in the lower force regions. It also imparts sufficient force to crush those particles with insufficient hardness thereby leading to the generation of fine powder. This fine powder prevents even airflow distribution, leads to higher sorbent bed airflow resistance, and can migrate through the packed bed leading to loss of bed integrity following rough handling and generation of fines that may be breathed by a respirator user.
In summary, two axis vibrational filling of a sorbent bed may lead to a desired packing density in the bulk of the entire sorbent volume but may also result in maldistribution of packing density in both axes, with attendant negative effects for targeted respiratory applications. Thus, there is a need for improved packing techniques to minimize or eliminate the aforementioned deficiencies in the current art.